We propose that the development of the secretory IgA (sIgA) system of the mammary tissue is regulated by factors other than direct antigenic stimulation of this tissue and that it is dependent on Gut Associated Lymphoid Tissue (GALT) for a source of IgA precursor cells committed to synthesis of antibodies (Ab) directed against intestinal antigens. Our major objectives are: a) to characterize the development of the secretory IgA (sIgA) system in mammary tissue of pregnant rabbits; b) to determine appropriate routes of immunization to elicit a major response to the IgA system of GALT and mammary tissue; and c) to determine if IgA precursor cells derived from GALT home to developing and/or lactating mammary tissue of rabbits. A fluorescent-Ab technique will be used to identify the time of major expansion of the IgA system in mammary tissue, and thereafter cell transfer studies will be done to test for mammary tissue homing of IgA cells in various stages of development. The dynamics of the IgA response to in vivo antigenic stimulation of GALT will be followed by means of PFC, RFC and immunofluorescent assays of lymphoid cell preparations from various tissues. In vitro cell culture to allow maturation of in vivo stimulated cells will be used to track the development of IgA precursor cells in various tissues, and results will be used to help identify characteristics of IgA cells involved in homing. Further studies relate to identification of factors regulating homing and/or development of IgA cells in mammary tissue.